Dichlorostyrene as accelerator in the polymerization of butadiene-1,3 with styrene



M. C. TAYLOR Nov. 7, 1950 0F BUTADIENE-l,3 WITH STYRENE 2 Sheets-Sheet 1Filed Dec. 30, 1948 N bm. QQ Qm Sm. QV. mm. QN ,9H 1 I /f/ ESE f www,IAO/Wil wf, /l ,f

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Nov. 7, 1950 M. c. TAYLOR 2,529,201

DICHLOROSTYRENE AS ACCELERATOR IN THE POLYMERIZATION 0F BUTDIENE-l,3WITH STYRENE Filed Dec. 30, `1948 2 Sheets-Sheet 2 ATTORNEYS PatentedNov. 7, 1950 DICHLOROSTYRENE AS ACCELERATOR IN THE POLYMERIZATION 0FBUTADIEN E-1,3

WITH STYRENE Maurice C. Taylor, Niagara Falls, N. Y., assignor toMathieson Chemical Corporation Application December 30, 1948, Serial No.68,134

2 Claims. (Cl. 26o-80.7)

This invention relates to improvements in the manufacture of copolymericmaterials by the copolymerization of butadiene and styrene, and moreparticularly provides improvements in the process for preparingmaterials of this type whereby the copolymerization reaction may be soaltered and accelerated as to increase the productive capacity ofapparatus of a given size and to improve the quality of the product.

The present application is a continuation in part of my copendingapplication Serial No.

510,928, filed November 19, 1943, now abandoned.

Synthetic rubber-like materials commonly designated synthetic rubber,have previously been prepared by the copolymerization of butadiene andstyrene. Such interpolymerization is usually accomplished in aqueousemulsion containing, in addition to water and the copolymerizationcomponents, such materials as emulsifying agents, emulsion stabilizers,catalysts for accelerating the reaction and sometimes other modifiers.

However, production of such rubber-like materials prior to my presentinvention has encountered numerous diiiculties. In the rst place, therate of reaction of the styrene and butadiene has been relativelyslowand. accordingly, the process has been excessively time consuming.'Further diiculties had been experienced with respect to the nature ofthe Synthetic rubber products. For example, in the unvulcanized state,most synthetic rubbers have been found to be decient in tackiness andability to adhere upon being pressed together. Also. aftervulcanization, they have beenlfound to be deficient in resilience andresistance to softening and deterioration by heat and usually to berelatively fiammable.

In recent years, a vast amount of research has been carried on having asits purpose the elimination or mitigation of such previously experienceddifficulties. A substantial improvement in the art is disclosed andclaimed in the copending application of John C. Michalek, Serial No.449,475, filed July 2, 1942, now abandoned, in accordance with whichcertain polymerizable nuclear chlorinated styrenes are used, instead ofthe styrene previously copolymerized with conjugated open chain dienesin the synthesis of such materials. A disadvantage in the substitutingof nuclear chlorinated styrene for styrene in such reactions is theadded cost of the nuclear chlorinated styrenes over the cost of styrene.

I have now discovered that. even if only a minor proportion of nucleardichlorostyrene be added to the monomeric mixture of styrene andbutadiene-1,3, various surprising results are o=b tained. I have found,for instance, that the polymerization rate under any given polymerizingconditions is materially and unexpectedly accelerated and that thecharacteristics oi the product are generally improved.

It has previously been found that, in the copolymerization of butadienewith styrene, the ratio of butadiene to styrene radicals in thecopolymeric product is usually greater than the proportion of thesematerials in the charge. This appears to be due to the fact that thebutadiene has a faster rate of reaction than has styrene under givenconditions. Whatever the cause, the product has generally been found tobe relatively richer in the butadiene radicals and poorer in styreneradicals.

Similarly, it has been found that, in the copolymerization of butadienewith nuclear dichlorostyrene, the ratio of the butadiene radicals to thedichlorostyrene radicals in the copolymeric product is generally lessthan the ratio of these materials in the charge. This appears to be dueto the extraordinary ease with which the dichlorostyrene is polymerized.

An advantage of my present invention is that, by my improved process, Ican. to a considerable extent, control the ratio of the variouscomponents in my product. I have found that, by adjusting the ratio ofthe dichlorostyrene to styrene, I can control the rate ofcopolymerization of my vinyl component relative to the rate ofcopolymerization of the butadiene and thus iniluence the ratio ofbutadiene radicals to vinyl radicals in the product. Further, in thisway, I have found it possible greatly to accelerate the overall rate ofcopolymerization.

Since the rate at which the butadiene copolymerizes with nucleardichlorostyrenes is much greaterthan its rate of copolymerization withstyrene, it might be expected that the rate .of copolymerization of thebutadiene with a mixture of styrene and nuclear dichlorostyrene would beproportional to the relative amount of these constituents of the vinylcomponent. Thus, by substituting an equal molar proportion, forinstance, of the dichlorostyrene for half of the styrene previouslyused, it might be expected that the rate of polymerization would beincreased by only 50% of the diiference in polymerization rate ofstyrene and dichlorostyrene, respectively, with the butadiene.

I have found, however, that when even a very small proportion of thedichlorostyrene is substituted for a like proportion of styrene, asurprisingly disproportionate change in copolymerization rate isobtained, the reaction proceeding at a much faster rate than couldreasonably be expected from the relative proportions of thedichlorostyrene and the styrene.

I am unable, at present, to explain or account for this surprisingdisproportionate increase in reaction rate. However, the results which Ihave obtained are graphically illustrated by the charts constituting theaccompanying drawings whereon the time required for the copolymerizationreaction in hours is plotted against theproportion of nucleardichlorostyrene, expressed in percentage by weight of the vinylcomponent.

In the operations illustrated on Chart A, the operating conditions werecomparable in every respect, excepting the composition of my vinylcomponent. The operations illustrated on Chart B were likewisecomparable in every respect, excepting the compositions of the vinylcomponent. However, the operating conditions of the operations of ChartB were such as generally to expedite polymerization rate by the use ofexpedients Well known today, but little known at the date of myinvention, While the operations on Chart A generally were carried outunder conditions not utilizing the more recently developed reactionaccelerating expedients.

As appears from Chart A, where the vinyl component consisted solely ofstyrene, the time required for copolymerization was 160 hours. Where myvinyl component consisted'solely of nuclear dichlorostyrene, thereaction time was about 22 hours. It would be expected that, where thevinyl component consisted of mixtures of styrene and dichlorostyrene,the reaction time would fall upon the straight, broken line connectingthese points, and decrease uniformly in proportion to the percentage ofthe dichlorostyrene used. vIt is shown, however, by these tests that byusing only relatively small proportions of the dichlorostyrene, thereaction time very sharply decreases following generally the solid lineof the chart. This sharp reduction in reaction rate continues untilabout 8 to 10% of dichlorostyrene has been substituted for the styreneand then the curve Atends to flatten out. Thus using as little as about8% by Weight of the dichlorostyrene and about 92% of styrene, thereaction time is reduced to about 40 hours, a reduction of about 75% inthe time required where styrene alone is used as the vinyl component ofthe butadiene-vinyl compound polymerization mixture. By substitutingstill larger quantities of dichlorostyrene for styrene, the reactiontime is fur ther reduced but at a markedly reduced rate. By increasingthe proportion of dichlorostyrene used beyond 8 to 10% by weight of thevinyl component, only a relatively small decrease in reaction time isattained.

As previously noted, the presence of very small proportions ofdichlorostyrene in the mixture is suiiicient to show this extraordinaryeiect. The use of about 3% or more by weight has generally been foundmaterially to reduce the reaction time and to give highly satisfactoryresults. I prefer to use no less than about 3%, but it will beunderstood that the 3% gure is not particularly critical. So long asenough dichlorostyrene is used to give a noticeable acceleration of thereaction rate, it is within the contemplation of the present inventioneven though somewhat less than 3%. Proportions of dichlorostyrene inexcess of about 8-10% do not give proportionate in shape to that ofChart A. The reaction time has, in all cases, been greatly reduced inthe runs of Chart B over that of the runs of Chart A by the use of moremodern reaction-accelerating conditions, in conjunction with the varyingof proportion of dichlorostyrene in the vinyl component. The solid vlineon Chart B was plotted from data from a series of runs, identical exceptfor a variation in the relative proportions of dichlorostyrene andstyrene used. In each run the composition of the reacting mixture was asfollows:

Component: Parts by weight Water 180.0 Soap 2.0 Dispersing agent 0.5Potassium persulfate 0.075 Sodium silicate solution (30%) 0.34 Dodecylmercaptan 0.4 Potassium ferro cyanide 0.1 Butadiene-1,3 '10.0styrene-dichlorostyrene component-. 30.0

In each of the runs, the soap, dispersing agent, persulfate, silicatesolution and ferro cyanide were dissolved in the Water. The dodecylmercaptan was dissolved in the styrene-dichlorostyrene component whichwas then emulsied with the aqueous solution. The resultant emulsion wascharged to an autoclave and the butadiene added under pressure.Agitation was maintained in the autoclave and the temperature thereinwas heldat 40 C. for a period of time suicient to l cause polymerizationto proceed to completion.

In the first of these runs, styrene alone was used as the vinylcomponent and under these conditions the copolymerization was 50%complete in 23.5 hours. Where 10% dichlorostyrene was substiuted for anequal weight of the styrene, 50% copolymerization was effected in 14.5hours. Where the proportion of dichlorostyrene was increased to 50% ofthe total vinyl component, time for effecting 50% copolymerization wasdecreased to 11.3 hours and where the vinyl component wasdichlorostyrene, time for effecting 50% copolymerization was 6.5 hours.

In the foregoing tests, the dispersing agent used was the sodium salt ofa condensed sulfonic acid marketed under the trade name Tamol MNO.

An important advantage of my present invention is this extraordinaryincrease in reaction rate occasioned by the use of a surprisingly smallproportion of the dichlorostyrene, thus making it possible to increasethe productive capacity of existing or proposed equipment byapproximately 4 or 5 folds, or conversely enabling one to produce agiven amount of copolymer in equipment one-fourth to one-fifth the sizepreviously required and at very little additional cost.

A further advantage is that, by reason of this acceleration of thereaction made possible by my present invention, it becomes commerciallypractical to use in such a copolymerization a wide variety of modifyingagents, the use of which had been impractical prior to my presentinvention because of their retarding effect on the copolymerizationrate. Such modifiers for example as butyl mercaptan, lauryl mercaptan,and the like, have been found to have important modifying effects on thecharacteristics of the rubber product, but also tend to decrease therate of reaction so that their use would normally be' attended ry a lossin capacity proportional to their retarding effect. By the process of mypresent invention, however, it is possible-to compensate more thanadequately for such retardation occasioned by the use of thesemodifiers. Thus, my invention makes practical the incorporation with thecopolymerization mixture of a considerably increased variety ofmodifying agents heretofore barred therefrom because of their retardlngeffect on the reaction rate.

In accordance with a further aspect of my present invention, the rate ofreaction of my vinyl component may, by properly proportioning theconstituents thereof, be so adjusted relative to the rate of reaction ofthe butadiene as to produce a. copolymer in which the ratio of the vinylradicals to the butadiene radicals is the same as the ratio of thesecomponents in the charge. Other desired ratios of the vinyl andbutadiene radicals in the product may similarly be effected.

It will be understood that the butadiene referred to herein and in theappended claims is the conjugated butadiene-1,3.

The nuclear dichlorostyrene used, in accordance with my presentinvention, may with advantage be the nuclear dichlorostyrenecharacterizd by a density (D425)` of 1.236 to 1.280 and a refractiveindex (Nn25) of from 1.5724 to 1.5838 described more fully in thecopending application of John C. Michalek, Serial No. 387,862, filedApril 10, 1941, now abandoned. It may include any of the pure isomers ormixtures thereof. for example, 2,3-, 2,4-, 2,5-, 2,6-, 3,4- or 3,5-dichlorostyrene.

The proportions of the butadiene and the vinyl component used inaccordance with my present invention, may be varied over a considerablerange with respect to each other. Advantageously the vinyl component, i.e., styrene plus dichlorostyrene. may represent about 20 to 50% byweight of the polymerizable components, i. e., vinyl component plusbutadiene. However, some advantages of the invention are attained evenwithout this range so long as the reaction is a copolymerization of thebutadiene-styrene type.

The polymerization reaction, in accordance with my invention, is withadvantage effected in aqueous emulsion as previously noted. The runsrepresented on Chart A. were made by the following general procedure.

The vinyl component and butadiene in the desired proportions are chargedto an autoclave equipped with a stirrer. There is also added water and asuitable catalyst, for example, hydrogen peroxide, urea peroxide,benzoyl peroxide, potassium persulfate, or sodium persulfate. Anemulsifying agent. an emulsion stabilizer, such as gelatin, glue, orcasein and, if desired, a modifying agent, such as ethylene dichloride,chloroform, carbon tetrachloride, or other closely related halogencompounds, and a surface tension regulator, such as capryl alcohol, ornormal octyl alcohol, are also charged to the autoclave. The autoclaveis then closed and heated to the reaction temperature for a period oftime sufllcient to complete the reaction, orto carry the lcopolymerization to the desired degree of completion. In normaloperation, the reaction is Seldom carried to completion, but is carriedto some point substantially short of completion. The polymeric materialis then separated from the remaining monomeric mixture and the latterused in a subsequent operation. After the reaction has been carried tothe desired degree of completion, the autoclave-is cooled, the copolymercoagulated by conventional methods, such as by freezing, acidifying, orsaiting out, and is separated from the mixture.

If desired, the emulsion may be prepared and subsequently charged to theautoclave or a solution of the accessory materials may be prepared inthe autoclave and the copolymerizing components subsequently added andemulsined therewith.

Emulsifying agents which may be used with advantage in my processinclude ordinary soap, that is, alkali metal salts of high molecularweight fatty acids, alkyl sulfates, alkali metal alkyl benzene, or alkylnaphthalene sulfonates, alkyl metal sulfo ethyl-oleate and salts ofother sulfonated esters and oils, as well as the more common soaps, suchas sodium, or ammonium oleate or laurate. In fact, ammonium oleate, orlaurate have been found to be particularly effective emulsifying agentsfor this purpose. ,The proportion of emulslfying agents used is notparticularly critical and is even less critical than where styrene aloneis used as the vinyl component. Proportions by weight ranging from about0.5 to about 15% of the principal reactive components of thecopolymerizing mixture have been used with advantage.

The proportion of catalyst employed in the process of my presentinvention is also less critical than in operations where styrene aloneis used as the monomeric vinyl component and may be varied within widelimits. Even in the absence of an accelerating catalyst, the reactionhas been found to proceed more rapidly than the reaction o1' thebutadiene with styrene when a catalyst is used. However, the reaction ofmy present invention proceeds even more rapidly where a catalyst such aspreviously mentioned is used and therefore the use of such catalyst isusually desix-able.

Water insoluble alcohols having from say 4 to 10 carbon atoms permolecule may be used as surface tension regulators. The proportions ofthese and other modifying agents used are likewise not critical and maybe varied over a considerable range as understood by the art. dependingupon the results desired. Suitable alcohols for this purpose includenormal octyl alcohol, capryl alcohol, and the like.

Various other modifying agents including anticross-linkers. such ascarbon tetrachloride, as well as other known types of modifying agentsincluding lauryl mercaptan, ethylene and other olefins may beincorporated in the emulsion.

It is desirable that the various components and reagents used inaccordance with my present invention be free from aldehydes since evensmall amounts of aldehydes appear to hinder the copolymerizationreaction. Generally, any aldehycles present in the various componentsmay be readily removed therefrom prior to use by treatment with acarbonyl reactive reagent, such, for example, as sodium bisulte,methabisulfte, sodium hydrosulte, or the like. Since only small amountsof aldehydes are ordinarily present in these constituents, treatmentwith solid bisulflte.

' or the like, serves to remove such impurities. It

is desirable to take the precaution of removing vany aldehyde present inorder that the copolymerization may proceed at the rapid ratecharacteristic of the copolymerization components of my presentinvention.

A further important advantage of my improved process is that thereaction may, if desired, be carried substantially to completion. It isgenerally recognized that, in such operations, the rate of reactionsubstantially decreases as the reaction approaches completion and, forthis reason, the reaction is frequently stopped short of completlon.However, because of the increased rate of reaction resulting indesirable products, the total required time is not unduly extended bycarrying the reaction substantially to completion.

In carrying out the operation, it is convenient to follow the course ofthe reaction by removing samples from time to time and acidifying,saltingout, or otherwise coagulating the reaction product. A clear,aqueous layer remaining after the coagulation, i. e., free fromunreacted hydrocarbons or dichlorostyrene indicates that the reaction iscomplete.

My invention will be further illustrated by the following specificexamples of its application in the production of my improved copolymericproduct. It will be understood, however, that these examples are forpurposes of illustration and that the invention is not limited thereto.In each instance the proportions are by weight.

Example I An aqueous solution was prepared by adding 4 parts ammoniumoleate, 1 part glue and 4.2 parts of sodium perborate to 250 parts ofwater. My vinyl component, comprising 28.2 parts of styrene and 2.48parts of nuclear dichlorostyrene and 0.05 part of benzoyl peroxide, werethen slowly added to the aqueous solution with stirring. The resultingemulsion was then charged to a rocking autoclave and 69.32 parts ofconjugated butadiene was charged under pressure to the autoclave. Themixture was held in the autoclave for 411/2 hours at a. temperature of75 C. with constantly maintained agitation. At the end of this period,the autoclave was opened, the emulsion diluted with about ten times itsvolume of water and acidied with diluted acetic acid until the emulsionwas broken. After coagulation, the copolymer was washed on a rubber milland dried. The dried product was found by analysis to have an iodinevalue of 232 and a toluene solubility of 51.3%. The molecular weight ofthe toluene soluble portion was found to be 67,400.

Example II An aqueous solution was prepared by adding 4 parts ammoniumstearate, 1 part glue and 4.2 parts of sodium perborate to 250 parts ofwater. There were emulsified with this aqueous solution 2.6 parts ofnuclear dichlorostyrene and 28.2 parts of styrene. Thereafter, theemulsion was charged to the autoclave together with 69.2 parts of theconjugated butadiene. After being held in the autoclave with agitationfor 59 hours at a temperature of 55 C., the reaction was found to becomplete. After washing and drying, the rubbery copolymer was found tohave an iodine value of 200 and a toluene solubility of 41%, the toluenesoluble portion having a molecular weight of 73,000.

In a comparable run from which the nuclear dichlorostyrene Was omittedand a correspondingly increased amount of styrene used, 180

hours was required for completion of the reaction.

The reaction temperature and the period of time required for completionof the copolymerization reaction are to a considerable extentinterdependent. The operating temperature may be varied over aconsiderable range, the optimum temperature being largely dependent uponthe components of the particular copolymerizing mixture.

An important advantage derived from the use of the present invention,particularly where the proportions of dichlorostyrene in the vinylcomponent approaches 8 to 10%, is that the product is more tacky in itsunvulcanized state and when pressed together adheres to a remarkabledegree, in this respect more normally resembling natural rubber. Theyare, likewise, more resistant to softening and deterioration by heat.The nonflammability of these products of my improved process as comparedwith synthetic products of the type previously available, is the furtherimportant advantage. By reason of this characteristic, they are lesslikely to ignite when exposed to fire and other sources of heat and arenot harmed under circumstances which would seriously damage natural orhalogen-free synthetic rubber compositions. The vulcanization of myimproved product, even further reduces its fiammability.

I have found products produced in accordance with the process of thepresent invention to be more susceptible to vulcanization andplasticization than are the previously available halogenfree syntheticrubbers. Relatively small amounts of a plasticizer compounded therewithyield highly plasticized products which are especially' suitable forpurposes such as the forming of thin nlm-like products and for coatingwires as an insulation. Articles prepared from the products of myimproved process are extremely iiexible and have improved resistance toheat. Further, these improved products, though thermoplastic aredeformed only at temperatures above those which render useless ordinaryhalogen-free synthetic rubbers. My products are particularly useful aswire coating compositions and have advantageously low power factors. l

It will be understood that the intended meaning of the terms polymerize,polymerizable, and polymerization as used herein, is not restricted tothe common dictionary definition, a union between two or more likemolecules to form another compound having the same elements in the sameproportions but a higher molecular weight and different physicalproperties, but that such terms are used herein in the more generalsense, as commonly used in the art, to include inter-polymerizationbetween unlike molecules, as indicated by the context.

I claim:

1. In the copolymerization of a mixture of monomeric materialsconsisting predominantly of butadiene-1,3 and styrene in which theconcentration of the monomeric materials in water approximates parts toabout 180 to 250 parts of water by weight and which contains about 0.5to 15% by Weight of the monomeric materials of an emulsifying agentselected from the class consisting of alkali metal salts of highmolecular weight fatty acids, ammonium salts of high molecular weightfatty acids, alkyl sulfates, alkali metal alkyl benzene sulfonates, andalkyl naphthalene sulfonates and in which a catalyst selected from theclass consisting of hydrogen peroxide, urea peroxide. benzoyl peroxide.potassium persulfate. sodium persulfate and sodium perborate isemployed. the improvement which comprises including in the emulsion.while it is being subjected to conditions producing copolymerization, aminor proportion oi` nuclear dichlorcstyrene, said dichlorostyrene beingpresent in an amount effective to accelerate the reaction rate. but notsubstantially in excess of 8 to 10% of the combined weight of thestyrene and dichlorostyrene. and maintaining said combined weight withinthc range of 20 to 50% of the total weight of the monomeric materials.

2. In the copolymerization of a mixture of monomeric materialsconsisting predominantly of butadiene-1,3 and styrene in which theconcentration of the monomeric materials in water approximates 100 partsto about 180 parte ci water by weight and which contains about 2 partsby weight of soap, about 0.5 part of a sodium salt or a condensedsulfonic acid, about 0.075 part potassium persulfate. about 0.34 part 10of 30% sodium silicate solution, about 0.4 part dodecyl mercaptan, about0.1 part potassium ferro cyanide. the improvement which comprisesincluding in the emulsion, while it is beingsub- .iected to conditionsproducing copolymerization, a minor proportion of nucleardichlorostyrene, said dichlorostyrene being present in'an amounteffective to accelerate the reaction rate, but not substantially inexcess of 8 to 10% o! the combined weight of the styrene anddichlorostyrene, and maintaining said combined weight within theapproximate ratio in parts by weight of 30 to '20 parts butadiene-1.3.

MAURICE C. TAYLOR.

REFERENCES CITED The following references are oi' record in the nie o!this patent:

1. IN THE COPOLYMERIZATION OF A MIXTURE OF MONOMERIC MATERIALSCONSISTING PREDOMINANTLY OF BUTADIENE-1.3 AND STYRENE IN WHICH THECONCENTRATION OF THE MONOMERIC MATERIALS IN WATER APPROXIMATES 100 PARTSTO ABOUT 180 TO 250 PARTS OF WATER BY WEIGHT OF THE MONOMERIC MATERIALSOF AN EMULSIFYING AGENT SELECTED FROM THE CLASS CONSISTING OF ALKALIMETAL SALTS OF HIGH MOLECULAR WEIGHT FATTY ACIDS, AMMONIUM SALTS OF HIGHMOLECULAR WEIGHT FATTY ACIDS, ALKYL SULFATES, ALKALI METAL ALKYL BENZENESULFONATES, AND ALKYL NAPHTHALENE SULFONATES AND IN WHICH A CATALYSTSELECTED FROM THE CLASS CONSISTING OF HYDROGEN PEROXIDE, UREA PEROXIDE,BENZOYL PEROXIDE, POTASSIUM PERSULFATE, SODIUM PERSULFATE AND SODIUMPERBORATE IS EMPLOYED, THE IMPROVEMENT WHICH COMPRISES INCLUDING IN THEEMULSION, WHILE IT IS BEING SUBJECTED TO CONDITIONS PRODUCTINGCOPOLYMERIZATION, A MINOR PROPORTION OF NUCLEAR DICHLOROSTYRENE, SAIDDICHLOROSTYRENE BEING PRESENT IN AN AMOUNT EFFECTIVE TO ACCELERATE THEREACTION RATE, BUT NOT SUBSTANTIALLY IN EXCESS OF 8 TO 10% OF THECOMBINED WEIGHT OF THE STYRENE AND DICHLOROSTYRENE, AND MAINTAINING SAIDCOMBINED WEIGHT WITHIN THE RANGE OF 20 TO 50% OF THE TOTAL WEIGHT OF THEMONOMERIC MATERIALS.